Topic: isocratic elution

During isocratic elution, the mobile phase elution strength within the column is constant throughout the entire separation process. This is how most liquid chromatography quality control methods are designed and it contrasts with gradient elution.

Naturally, any unintended changes of eluent composition will affect the retention. In ion chromatography, which often use hydroxide eluents or carbonate-bicarbonate eluents that has very limited buffer capacity, it is therefore often important to protect the eluent solution from contamination by foreign ions. Glass bottles, which have a tendency of releasing ions from it surfaces, may therefore often not be a suitable choice for eluent storage. In addition, these eluents often need to be protected from carbon dioxide in the air to avoid contamination by carbonate species.

To learn more, browse the application examples below, return to the knowledge overview, or contact Diduco to discuss your specific analysis.

Applications

ion chromatography

Published case study of analytical quality by design method development and validation

Diduco has published a scientific peer-reviewed case study on how modern analytical method development can be performed in the pharmaceutical industry. The work was performed according to analytical quality by design (AQbD) principles to establish the design space and robust setpoint of the ion chromatography assay, and then validated according to the guidelines established by the International Council for Harmonization (ICH).

ion chromatography

Preserving eluent quality with dedicated storage protected from ambient carbon dioxide

To ensure that liquid chromatography analysis methods meet regulatory demands of retention repeatability as dictated by pharmacopoeia and the ICH guidelines, it is important to protect weakly buffered eluents from ambient carbon dioxide. The formation of carbonate species will otherwise change the pH and strength of the eluent, thus shifting retention.

ion chromatography

Screening of contaminants and forced degradation products in lithium ion battery electrolyte

Electrolytes in rechargeable batteries for cars, mobile phones, and other portable electric devices typically contain negatively charged counterions that together with lithium and a non-aqueous solvent form an ionic liquid. The bis(fluorosulfonyl)imide anion is a rather new ionic liquid constituent which thus need new quality control procedures.

ion chromatography

Analysis of dietary supplement capsules with carnitine using a generic method for counterions

Oral L-carnitine is a dietary supplement that has been shown to reduce fatigue in elderly people with low muscular endurance, but its effects on athletes during physical activity are not well-supported. Although this endogenous compound is well-known for its involvement in the mitochondrial oxidation of long-chain fatty acids, no scientific evidence has been found that carnitine in isolation enhances fat-burning.

ion chromatography

Determination of sulfamate and sulfate in topiramate tablets according to USP monograph

Official quality control method for the second-generation antiepileptic drug topiramate which also have shown effect against migranes. This analysis was performed according to the United States Pharmacopeia monograph and determines the degradation products sulfamate and sulfate which can be formed during storage in humid environments or at elevated temperatures.

ion chromatography

Comparing suppressed and non-suppressed ion chromatography

Suppressed ion chromatography with conductivity detection is a powerful and sensitive technique to analyse charged ionic species, especially anions of strong acids. The chemically regenerated membrane suppressor Xenoic® XAMS can enable analysis of such anions down to levels of a few microgram per litre (part per billion, ppb).

HILIC

Separation of simple sugars and carbohydrates

Simple carbohydrates are frequent ingredients in drinks, food, dietary supplements and pharmaceutical formulations. One approach to their analysis is hydrophilic interaction chromatography combined with evaporative light scattering detection, although this might be challenging due to the possibility of reducing sugars to mutarotate and thereby change their conformation into other anomers with different retention.

HILIC

Separation of nucleosides and nucleobases

Being one of the basic components of all cells as building blocks of DNA and RNA, there is a high and growing need for bioanalytical methods to determine nucleosides, nucleobases and related compounds in a variety of samples. Hydrophilic interaction chromatography is one of the most suitable approaches for this, due to the hydrophilicity of these compounds as demonstrated by their negative logP and logD values.

ion-exclusion chromatography

Separation of organic acids by ion-exclusion chromatography

Separation of organic acids can be a challenging task due to their hydrophilic nature and structural diversity. One of the more traditional approaches to this analysis is ion exclusion chromatography, which offer complementary selectivity to other separation techniques, especially for the monovalent acids which tend to be more strongly retained in this mode.

reversed-phase

Analysis of cannabinoids in dried industrial hemp after methanol extraction

The legislation in many countries allow cultivation of industrial hemp provided that the strains do not produce high amounts of tetrahydrocannabinol (THC) and other psychoactive cannabinoids classified as narcotic substances. These strains of cannabis sativa are instead typically rich in compounds such as cannabidiol (CBD) and cannabidiolic acid (CBDA).

reversed-phase

Reaction monitoring of enzyme-catalysed one-pot cascade synthesis

The move towards a more sustainable world includes sourcing functional monomers for polymer synthesis from renewable natural products rather than from fossil-based sources. This green chemistry revolution often relies on the development of new reaction procedures efficiently catalysed by enzymes to involve fewer harmful chemicals.

ion chromatography

Modernized assay for foscarnet following ICH guidelines

New preliminary assay for the antiviral medication foscarnet which is a DNA polymerase inhibitor that is used to combat herpes viruses, including drug-resistant cytomegalovirus, and to treat patients with HIV as part of salvage therapy. This method was developed by Diduco to meet the requirements in the ICH guidelines, as a contribution to the United States Pharmacopoeia initiative for modernized monograph methods.

ion chromatography

Quantification of common anions in bottled drinking water according to EPA method 300.1A

Official procedure for quality control of drinking water according to the United States Environmental Protection Agency. This procedure allows quantification of the seven common inorganic anions fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulfate in the ranges recommended by WHO and national authorities.

ion chromatography

Generic method for isocratic separation of fifteen common pharmaceutical counterions

Many medicines and dietary supplements are bases that carry a positive charge, and consequently these small molecules are accompanied by negatively charged counterions. Such anionic excipients may influence the properties of the pharmaceutical formulation and can also influence the effect of the active ingredient since different ion pairs can have different dissolution rates or abilities to penetrate cell walls.

ion chromatography

Analysis of dietary supplement capsules with glucosamine using a generic method for counterions

Oral glucosamine is a dietary supplement that is marketed to support the structure and function of joints and claimed to provide pain relief for people with arthritis and osteoarthritis, although there is no clear evidence that its benefit is significantly above placebo.

ion chromatography

Alternative method for determination of voriconazole impurity E

Voriconazole is an antifungal medication that is included on the WHO Model list of Essential Medicines. During synthesis of the active ingredient a resolving agent for chiral amines is often used, and it is thus necessary that the quality control prove that this substance is not present at harmful levels in the final product.

ion chromatography

Isocratic separation of four small monovalent organic acids using a weak hydroxide eluent

Singly charged anions of small organic acids can be challenging to separate due to their low retention on many ion chromatography columns. During method development for their analysis several different columns often need to be compared to find a separation selectivity that is suitable for the set of compounds in question.

ion chromatography

Generic method for isocratic separation of ten common pharmaceutical counterions

ion chromatography

Quantification of common anions in drinking water according to EPA method 300.0A

Older version of the official procedure for quality control of drinking water according to the United States Environmental Protection Agency.

ion chromatography

Partial separation of structurally similar organic acids at isocratic conditions

Small organic acids are an important group of chemical compounds that needs to be analysed and quantified in many different industries. This application shows ion chromatography of a variety of organic acids using a non-optimized isocratic carbonate-based eluent.

ion chromatography